In the drilling and completion industry, the formation of boreholes for the purpose of production or injection of fluid is common. The boreholes are used for exploration or extraction of natural resources such as hydrocarbons, oil, gas, water, and alternatively for CO2 sequestration.
When a liner is run through casing in the borehole, the liner is supported within the casing by a liner hanger. Hydraulically set liner hangers have been developed that deploy slips radially outwardly when internal pressure is built up on a dropped ball. The internal pressure acts against a bias force on each slip toward the retracted position. The hanger is set when internal pressure is applied to the liner hanger's cylinder which extends the slips against the casing. When coupled with set down weight on the mandrel, the weight of the liner is then supported by the extended slips that bite against the surrounding casing.
Cement is used to seal tubulars, such as the liner, in the borehole and prevent fluid and gas migration. The cement is pumped through a one way valve, such as a float collar or float shoe, at the lower end of the string to be sealed. Float collars and float shoes prevent heavier uncured cement in the annulus from u-tubing back into the liner when displacement is complete. The pumped cement needs to be displaced from the tubular to the surrounding annulus after it is delivered from the surface. Different wiper plug systems have been devised to push the cement ahead of the plug until the plug is bumped on a landing shoulder in the vicinity of the shoe.
Liner wiper plugs are typically suspended at the top of a liner to be cemented with an open passage through the wiper plug through which the cement is delivered. A dart is then landed in the wiper plug and the two travel together to wipe the liner free of cement until the plug is bumped. The plug can have extending fins in parallel rows or it can be a solid block. One or two plug systems can be used and in each case a dart lands in the plug to move the two in tandem. Composite materials have been employed in such plugs to speed up milling that occurs after the plug or plugs are bumped and the cement sets. The normal procedure is to drill out the plug or plugs and the shoe and either extend the well or complete the well.
Usually run in the liner one or two joints above a float collar or shoe, one type of landing collar provides the seat and latch profile to catch the liner wiper plug at the completion of cement displacement. Landing collars and plugs are designed to ensure rapid and complete drillout. Another type of landing collar has all of the features of the first type of landing collar, and also includes an integral ball seat below the liner wiper plug seat. When a setting ball is dropped and seated, pressure may be applied to activate hydraulic devices in the liner string, such as hydraulic-set liner hangers and external casing packers. Further increase in pressure shears out the ball and seat, restoring full circulation through the shoe for cementing operations.
The art would be receptive to alternative devices and methods for landing collars to provide variety and improvement in cementing operations.